Analysis of fluids is useful in many applications. For example, measurement of water's hardness may be of importance, as hard water may be undesirable in certain contexts. Accordingly, colorimetric methods for analyzing water hardness have been developed. Colorimetery uses a color change in the sample fluid as representative of an amount of a substance of interest, e.g., a component in an aqueous sample fluid that reacts with a reagent to form a colored product. The colored product may be measured by light absorbance.
It has been observed that in certain cases colorimetric measurements of water vary away from an expected linear response. That is, the amount of color change does not linearly correspond to the amount of substance of interest. Many factors may contribute to this. For example, a sample's volume, the indicator (color) amount added to a sample, the reagent solubility in the sample, etc., may affect the measured color such that it varies away from a linear response. This variation away from linearity often takes place at the ends of the measurable range (e.g., high and low ends of the measurable range). The variation away from linearity causes inaccurate measurement.